The present application relates to a battery pack and a control method for a battery pack for detecting internal short-circuiting of battery cells.
In recent years, portable electronic devices such as notebook personal computers (PCs), cellular phones and personal digital assistants (PDAs) have been in widespread use, and lithium-ion secondary batteries have been widely used as power sources for the devices because of their advantages such as high voltage, high energy density and lightweightness.
Battery cells of lithium-ion secondary batteries may be deteriorate or heat up abnormally if the lithium-ion secondary batteries are overcharged to a voltage above a predetermined voltage when they are charged or overdischarged to a voltage below a predetermined voltage when they are discharged. Therefore, a battery pack containing a lithium-ion secondary battery is generally equipped with a protection circuit for protecting the battery from being overcharged and overdischarged.
In general, such a protection circuit measures the charge and discharge currents of the secondary battery and the voltage of each block of the battery cells to detect an abnormality such as overcharging, overdischarging or abnormal cell balance on the basis of the measurement results. When it is determined from the detection results that the battery cells are abnormal, the protection circuit performs a protection operation such as prohibiting charging and discharging of the secondary battery.
In addition, when a battery pack containing a secondary battery is subjected to abnormal charging and discharging repeatedly, or to an external stress which deforms the cells inside, or when foreign matter enters the battery cells, an abnormality due to short-circuiting may occur in the battery cells. When an abnormality due to internal short-circuiting occurs, the protection operation based on the detection process and detection results discussed above may not be sufficient, and the short-circuiting inside the battery cells may lead to a serious accident such as fire produced from the battery pack.
In order to address the foregoing issue, various schemes have recently been proposed to detect an abnormality of battery cells due to internal short-circuiting. For example, Japanese Patent No. 3437823 discloses a method in which the voltages of cell blocks are measured, and an abnormality due to short-circuiting in battery cells is detected according to whether or not the difference between the maximum voltage and the minimum voltage continues to be a predetermined threshold or more for a prescribed time.